Three groups cooperate in this program. The group under D. Mazia is studying the following aspects of the assembly and function of the mitotic apparatus. The continuity of centrosomes, the problem of the origin of centrosomes (and centrioles) in artificial parthenogenesis; bipolarization, the separation of centrosomes; chromosome condensation in relation to the osmolarity of cytoplasm; chromosome behavior in a monopolar mitotic apparatus (splitting of chromosomes and the question of the generation of microtubules by kinetochores); the "cytostatic factor" (factor which arrests mitosis at metaphase), its molecular character and its presence of various phases of the mitotic cycle; synchrony of mitosis in several nuclei in the same cytoplasm, effects of near-ultraviolet irradiation; fusion of sea urchin eggs with each other and with other cells; calmodulin in the regulation of Ca levels dividing sea urchin eggs. The group under F. Wilt is studying the molecular biology of early development of sea urchin embryos, with emphasis on proteins of chromatin and on mRNAs. The stability of mRNAs for histones in both nuclei and cytoplasm at various stages of development is being probed. The differences in the prevalent mRNA classes in different cell types in the differentiating embryo will be investigated. Using methods for the separation of the cell types, possible differences in the non-histone proteins will be analyzed. The spicules of the skeletons of sea urchin larvae will be used as an accessible model of advanced differentiation; the numbers and kinds of proteins and glycoproteins will be investigated. R. Strohman's group will continue studies of gene regulation during terminal differentiation in skeletal muscle cells in vitro. Measuring the synthesis of myosin heavy chains (MHC) they are studying the levels of mRNA for MHC at various stages of differentiation. Another line of investigation deals with the effect of sustained relaxation, in the presence of tetrotoxin, on the turnover of MHC in muscle cell cultures. Research on the effects of Diazepam (Valium) on myoblast fusion and on the accumulation of myofibrillar proteins is to be extended, including work on human myoblasts.